Robots are employed in a variety of industrial work operations, and excel in operations that require a high amount of precision and consistency. Exemplary robotic work operations include welding, cutting, grinding, and painting. To perform a particular operation, a specified work tool is typically mounted to an operative end of a robot arm.
For example, a welding torch is mounted onto a robot arm to enable robotic welding operations. Welding operations require precision movements that are particularly well-suited for robotic manipulation. Accordingly, robots have been increasingly used for welding purposes.
One difficulty encountered in robotic work operations, including welding operations, arises from tolerances in aligning and fixturing work pieces. In particular, if a work piece is even slightly misaligned, the robot must be reconfigured to account for the misalignment. To overcome this difficulty, robotic systems often employ a control mechanism that adjusts the robotic work operation to compensate for alignment and fixturing tolerances. A common control mechanism is an optical sensor with a feedback control circuit. The optical sensor obtains information about the work piece alignment and the feedback control circuit uses the information to adjust the work operation accordingly.
A key element of the control system described above lies in the ability of the optical sensor to obtain data from the work piece. In welding operations, for example, the optical sensor must be manipulated by the robot to observe the weld zone and surrounding areas. To this end, prior art systems employ an optical sensor that is directly and permanently mounted on the torch. For example, U.S. Pat. Nos. 3,594,540, 4,215,299, and 4,624,301 show robotic welders having sensing devices permanently affixed to the welder. Such a design allows the sensor to always be available. However, there are several drawbacks to mounting the sensor permanently to work tool. First, sensors tend to be bulky, and can restrict access and articulation of the robot arm during a welding operation. Second, certain work operations can damage the sensor. For example, welding operations produces fumes, spatter, and heat which can damage a sensor when mounted on or near the welding torch.
A solution that overcomes the shortcomings of permanently mounting the sensor to the welding torch is a solution in which the work tool is interchanged with a sensor unit. Specifically, the robot may pick up the sensor, move the sensor to a position in which it can gather data, replace the sensor on a docking device, and then pick up and manipulate the work tool. A disadvantage of interchanging the welding torch or work tool with the sensor is that the interchange process is time consuming. In particular, the discrete steps of picking up and setting down the work tool and picking up and setting down the sensor increases the time required to complete the work operation.
What is needed, therefore, is an apparatus and method for mounting a sensor to a work tool attached to a robot arm which overcome one or more of the above-mentioned drawbacks.